Radio shielded spark plug



Filed March 27, 1937 tallic shell or casing I9, Figure 6, within which there ls a lining or insulating material 20 such as mica, a tube of molded plastic material, or equivalent substance. The insulating member made up of the metallic casing I9 and its lining of insulating material form a single element which is removable as a unit from and replaceable in the tubular shield I6 and the lower end of which rests upon an inwardly extending ledge at the lower end of the shield tube, and the upper end of which terminates slightly below the upper end of said shield; and the insulating member iits somewhat loosely in the shield so as to be easily removable therefrom and replaceableand more or less surrounding the adjacent ends of said parts there is a sealing composition 24, which is conductive to a degree such that high tension current can flow therethrough; and 25 designates the grounded or shell electrode of the plug. The upper end of the insulating member extends upward and into the insulating member Il and shield tube I5 and is tubular, as shown, and a coil spring 26 ishoused within the cylindrical passage in said extending portion and projects slightly above the upper end of` the insu-V lating member. The lower end of this spring contacts with the upper end of the electrode part 23 so that current is supplied to the central electrode through said spring.

The numeral 21 designates a connecter whereby current is supplied to the central electrode, the same having a depending part l28 which enters the upper part of the tubular insulating member IB and has a screw 29, the head of which contacts with the upper end of the spring 26 when the connecter 21 is secured to the tubular shield I6 as shown. 'I'his connecter has an internally threaded neck 30; and 3l is a tubular nut carried by the tubular shield and the upper end of which engages a iiange 32 at the upper extremity of said tubeand secures the connecter 21 thereto as will be understood.

The lower end of the spring 2B engages with the inner wall ci.' the passage in the insulating member in which it is housed so that the spring remains in the passage when the connecter 21 is detached from the tubular shield I6 and removed from the plug structure, which has often Vto be done, so that the spring is protected from injury both by its position within said passage and the fact that it is located well down within the shield tube I6. Removal of the connecter, therefore, does not expose a delicate contact spring and render it liable to injury as has heretofore been the case when an equivalent spring has been carried by and removed with a connecter, like the connecter 21, when the same is removed from a shielding tube. This holding action may be readily accomplished by bending the extremity of the lower whorl or convolution of the spring outward slightly from the` cylindrical boundary ot the spring, as indicated at 3,3, Fig.

ure '7, so that said end will press outward against the interior of the passage within which it is located and thus hold the spring within said passage.

In the forms of my invention illustrated in Fig ures 2 and 3 the annular resilient member l5 which holds the insulating member ll in place within the shell or casing 34 is itself held in place by an inturned holding flange 35 and a metallic gasket 36, as in single piece spari: plugs; said member being compressed and loaded sufficiently to insure a continuously acting force upon the insulating member throughout the life oi the plug by a die member which turns a flange at the 'upper end of the shell inward and into holding engagement with. the gasket 3B; the diiierence between the two forms being that ln Figure 2 the lower end of the 4tubular shield is fastened to the shell by a gland nut 31, whereas in Figure 3 the lower end of the shield is welded to the upper end oi' the shell or casing of the plug.

Figure 4 illustrates a variation of my invention wherein the annular resilient member i5 is compressed and loaded by a ring 3B channel-shaped in cross-section and to which pressure is applied by a suitable press and, While the ring contacts with the upper end of the shell and the member l5 is in a stressed condition, the ring is welded to the shell as indicated by the numeral 38; the shield being welded to the ring so as to be in eilect an integral part of the shell or casing in this, the same as in the other forms of my invention hereinbefore described.

Having thus described and explained my invention I claim and desire 'to secure by Letters Patent:

l. In a radio shielded spark plug, a hollow metallic shell or casing; a tubular metallic shield carried by said shell; an insulating member within said shell and extending into said shield, and which insulating member is held in place within said shell by said tubular metallic shield; a passage extending longitudinally oi said insulating member and the outer part of which is cylindrical in form; a central electrode within said passage; and a coil spring within the outer cylindrical part oi said passage and extending beyond the outer end of said insulating member, and which spring contacts `with said central electrode so as to supply current thereto.

2. In a radio shielded spark plug, a hollow metallic shell or casing; a tubular metallic shield carried by said shell; an insulating member within said shell and extending into said shield, and which member has an annular shoulder and a longitudinally extending passage; a central electrode within said passage; means for supplying current to said central electrode; and an annular resilient metallic member C-shaped in crosssection secured in place within said shell between the lower end of said shield and said annular shoulder and surrounding said insulating member, and which resilient member engages said shoulder to thereby hold said insulating member in place within said shell.

3. In a radio shielded spark plug, a hollow metallic shell or casing; an insulating member within said shell and extending upwardly therefrom, and having an annular shoulder and a longitudinally extending passage; a central electrode within said passage; means for supplying current to said central electrode; an annular resilient metallic member C-shaped in cross-section within said shell and surrounding said insulating member and the lower end of which engages the shoulder aforesaid; and a tubular metallic shield carried by said shell and surrounding the upper end of said insulating member, andthe extremity of which engages the upper end of said annular resilient member and holds it in place within said shell.

4. In a radio shielded spark plug, a hollow metallic shell or casing; a tubular metallic shield carried by said shell; an insulating member within said shell and extending upwardly therefrom, and having a longitudinally extending passage; means for holding said insulating member in place within said shell; a central electrode within the passage aforesaid; means for supplying current to said central electrode; and a removable tubular insulating member within said tubular shield, said insulating member comprising an outer metallic casing and an inner lining of im sulating material within said outer casing, the ends of said outer casing being turnedinwardly so as to embrace the extremities of said insulating liningl to thereby protect said ends.

HECTOR RABEZZANA. 

